1. Field of the Invention
This invention relates to a continuously variable transmission which can continuously change the transmission ratio between an input shaft and an output shaft, in various industrial machines including automobiles.
2. Related Background Art
Various types of continuously variable transmissions are used and one of them is a toroidal type continuously variable transmission. This is a transmission in which the opposed surfaces of an input disc mounted on an input shaft and an output disc mounted on an output shaft are formed by toroidal surfaces. A power roller is disposed between these toroidal surfaces, and by changing the rocked state (angle) thereof, the transmission gear ratio between the input shaft and the output shaft can be changed.
FIGS. 1 and 2 of the accompanying drawings show a conventional toroidal type continuously variable transmission described in Japanese Utility Model Laid-Open Application No. 1-173552. An input side disc 2 and an output side disc 4 are rotatably supported around a tubular input shaft 15 through needle bearings 16. Also, a cam plate 10 is spline-engaged with the outer peripheral surface of an end portion (the left end portion as viewed in FIG. 1) of the input shaft 15 and is prevented from moving away from the input side disc 2 by a flange portion 17. This cam plate 10 and rollers 12 together constitute a pressing device 9 of the loading cam type for rotating the input side disc 2, on the basis of the rotation of the input shaft 15 while pressing the input side disc 2 toward the output side disc 4. An output gear 18 is coupled to the output side disc 4 through a key 19 so that the output side disc 4 and the output gear 18 may be rotated synchronously with each other. The output gear 18 is rotatably supported by a bearing 41.
The opposite end portions of a pair of trunnions 6 are supported by a pair of supporting plates 20 for rocking about an axis X--X and for displacement in X--X direction (the front to back direction as viewed in FIG. 1 or the left to right direction as viewed in FIG. 2). Displacement shafts 7 are rotatably supported in circular holes 23 formed in the intermediate portions of the trunnions 6 through needle bearings 24. Also, power rollers 8 are rotatably supported around pivot shaft portions 22 through needle bearings 25.
The pair of displacement shafts 7 are provided at opposite side positions relative to the input shaft 15, and the pivot shaft portions 22 are eccentric relative to support shaft portions 21. The direction of eccentricity is the same direction (the right to left direction as viewed in FIG. 2) in the rotational direction of the input side and output side discs 2 and 4 and a direction substantially orthogonal to the lengthwise direction of the input shaft 15. Accordingly, the power rollers 8 are somewhat displaceable in the lengthwise direction of the input shaft 15.
Thrust ball bearings 26 and thrust needle bearings 27 are provided between the outer side of the power rollers 8 and the inner side of the intermediate portions of the trunnions 6. The thrust ball bearings 26 support a load in a thrust direction applied to the power rollers 8, and yet permit the rotation thereof. The thrust needle bearings 27 support a thrust load applied from the power rollers 8 to outer races 30, and yet permit the pivot shaft portions 22 and the outer races 30 to rock about the support shaft portions 21.
Driving pistons 37 are secured to the outer peripheral surfaces of the intermediate portions of driving rods 36 coupled to one end portion (the left end portion as viewed in FIG. 2) of the trunnions 6, and are fitted in an oil-tight manner in driving cylinders 38. Consequently, the rotation of the input shaft 15 is transmitted to the input side disc 2 through the pressing device 9, and the rotation of this input side disc 2 is transmitted to the output side disc 4 through the pair of power rollers 8, and further the rotation of this output side disc 4 is output via the output gear 18.
When the rotational speed ratio between the input shaft 15 and the output gear 18 is to be changed, the pair of driving pistons 37 are displaced in opposite directions. With this, the pair of trunnions 6 are displaced in opposite directions (for example, the lower power roller 8 in FIG. 2 to the right and the upper power roller 8 to the left). As the result, the direction of a force in the tangential direction acting on the portions of contact between the peripheral surfaces 8a of these power rollers 8 and the inner sides 2a and 4a of the input side disc 2 and the output side disc 4 changes. With this change, the trunnions 6 rock in opposite directions about a pivot shaft X--X pivotally supported by the supporting plates 20.
When the transmission of the rotational force is thus effected between the input shaft 15 and the output gear 18, the power rollers 8 are displaced axially of the input shaft 15 on the basis of the resilient deformation of each constituent member, and the displacement shafts 7 are slightly pivotally moved about the support shaft portions 21. As the result, the outer sides of the outer races of the thrust ball bearings 26 and the inner sides of the trunnions 6 are displaced relative to each other.
Further, there is known a structure (double cavity type) in which to increase transmittable torque, as shown in FIG. 3 of the accompanying drawings, input side discs 52A, 52B and output side discs 54A, 54B are disposed at the opposite ends of an input shaft 65 to be parallel to one another with respect to the direction of transmission of power. These output side discs 54A, 54B are mounted around the input shaft 65 through bearings 66 to thereby make the rotation thereof relative to the input shaft 65 and the displacement thereof in the axial direction of the input shaft 65 possible. The input side discs 52A, 52B are supported for axial movement relative to the input shaft 65 and for rotation in a circumferential direction with the input shaft. An output gear 68a is rotatably supported on the intermediate portion of the input shaft 65, and the output side discs 54A, 54B are spline-engaged with the opposite end portions of a cylindrical portion provided in the central portion of the output gear 68a.
One (the left as viewed in FIG. 3) input side disc 52A has its back abutted against a loading nut 89 through a belleville spring 95 having a great resilient force (in some case, abutted directly against the loading nut) to thereby substantially prevent the axial displacement thereof relative to the input shaft 65. In contrast, the input side disc 52B opposed to a cam plate 60 is supported on the input shaft 65 by a ball spline 90A for axial displacement, and a belleville spring 91 and a thrust needle bearing 92 are provided in series between the back (the right surface as viewed in FIG. 3) of the input side disc 52B and the front surface (the left surface as viewed in FIG. 3) of the cam plate 60. The belleville spring 91 serves to impart a pre-load to the portions of contact between the inner sides 52a, 54a of the discs 52A, 52B; 54A, 54B and the peripheral surfaces 58a of power rollers 58, and the thrust needle bearing 92 serves to permit the relative rotation of the input side disc 52B and the cam plate 60 during the operation of a pressing device 59.
As shown in FIG. 3, in a toroidal type continuously variable transmission of the so-called double cavity type, one or both of the input side discs 52A, 52B opposed to the cam plate 60 are supported for axial displacement relative to the input shaft 55 by ball splines 90A, 90B. The purposes of this are:
(i) To completely synchronize the rotations of the input side discs 52A, 52B with each other; and PA1 (ii) To endow the function of item (i) above, and yet permit the input side discs 52A, 52B to be axially displaced relative to the input shaft 65 on the basis of the resilient deformation of each constituent member resulting from the operation of the pressing device 59.
The ball splines 90A, 90B are provided with inner diameter side ball spline grooves 96 formed in the inner peripheral surfaces of the input side discs 52A, 52B, the same number of outer diameter side ball spline grooves 97 as the spline grooves 96 formed in the outer peripheral surface of the intermediate portion of the input shaft 65, and a plurality of balls 98 provided for rolling between the two. As regards the ball spline 90A for supporting the input side disc 52B, a restraining ring 88A is restrained in a restraining groove 99A formed in the portion toward the inner side 52a of the inner peripheral surface of the input side disc 52B to thereby prevent the plurality of balls 98 from being displaced toward the inner sides 52a of the input side discs 52A, 52B and slipping out from between the inner diameter side and outer diameter side ball spline grooves 96 and 97. As regards the ball spline 90B for supporting the input side disc 52A, a restraining ring 88B is restrained in a restraining groove 99B formed in the outer peripheral surface of the intermediate portion of the input shaft 65 to thereby limit the plurality of balls 98 being displaced toward the inner side 52a of the input side disc 52A.
Also, when in a toroidal type continuous variable transmission incorporating a loading cam device therein, input torque is small and a torque difference is created between a cam disc and an input disc, the urging force of the input disc toward a power roller may sometimes be deficient and the power roller may idly rotate. Therefore, a pre-load force generating device such as a belleville spring is provided between the cam disc and the input disc to thereby make up for a pressing force toward a torque input shaft (see the belleville springs 91 and 95 of FIG. 3).
The pressing force of the input disc toward the torque input shaft by the above-mentioned pre-load generating device is minimum in a state in which during stoppage or during steady rotation or the like, little or no torque difference is created between the cam disc and the input disc, and is designed to continuously increase in conformity with a torque difference created between the two discs. Accordingly, when the loading cam device is to be incorporated into the toroidal type continuously variable transmission, it is necessary to correctly dispose rolling members in the recesses of the two cam surfaces of the cam disc and the input disc. In order to accomplish this incorporating work easily, it is known to provide the loading cam device with a tentative assembling mechanism capable of integrally fixing the recesses of the two cam surfaces of the cam disc and the input disc in advance in a state in which their positional relation is uniformized so that they may correspond to the rolling members held by a holder.
As the tentative assembling mechanism of this kind, one using a knock pin and one using a threaded hole and a bolt are disclosed in Japanese Patent Laid-Open Application No. 4-351361. When the knock pin is used, the knock pin is inserted into a pin hole extending through the cam disc, the holder and the input disc, and the cam disc, the holder and the input disc are fixed integrally with the pre-load generating device by a frictional force between the knock pin and each pin hole. Also, when the threaded hole and the bolt are used, through-holes are formed in the cam disc and the holder and a threaded hole is formed in the input disc, and the bolt is screwed into the threaded hole of the input disc through the through-hole to thereby fix the cam disc, the holder and the input disc integrally with the pre-load generating device.
If this is done, the rolling members can be prevented from escaping the recesses of the two cam surfaces of the cam disc and the input disc, so that the loading cam device can be reliably incorporated into the toroidal type continuously variable transmission in a state in which the generated pressing force is minimum.
In the case of the above-described conventional structure of FIGS. 1 to 3, however, the work of restraining the restraining ring 88A in the restraining groove 99A formed in the inner peripheral surface of the input side disc 52B on the pressing device 59 side has been cumbersome, and this has contributed to high cost of the toroidal type continuously variable transmission. That is, after the input side disc 52B is fitted around the intermediate portion of the input shaft 65, a gap large enough to pass the restraining ring 88A therethrough does not exist between the inner peripheral surface of the input disc 52B and the outer peripheral surface of the input shaft 65. Therefore, it is necessary to mount the restraining ring 88A in the restraining groove 99A prior to fitting the input side disc 52B around the input shaft 65. The plurality of balls 98 are lightly secured to the outer diameter side ball spline groove 97 in advance by grease or the like, and in that state, the input side disc 52B is fitted around the ball spline groove 97.
The, the lubrication of the internal mechanism of the toroidal type continuously variable transmission including the ball spline 90A is done by traction oil, so that it would be unnecessary to apply grease to the outer diameter side ball spline groove 97 but for the work of lightly securing the plurality of balls 98 by the grease or the like to assemble the input side disc 52B to the input shaft 65 with the restraining ring 88A mounted in the restraining groove 99A.
When, the above-described toroidal type continuously variable transmission is to be assembled, various constituents (such as the input shaft and the input and output discs) have heretofore been successively assembled inside a housing 40 (FIG. 2) for containing the body of the transmission. Accordingly, the deviation of the positional relation of each portion based on the integration of the dimensional error of each constituent and whether each constituent will properly function after assembly could be confirmed only after these constituents have been actually assembled in the housing 40.
In addition, to secure the operational efficiency and durability of the continuously variable transmission, the positional relations among the constituents must of course be maintained highly accurate. Therefore, when the deviation of the positional relation of each portion becomes great beyond a predetermined limit due to the integration of the dimensional error of each constituent, the continuously variable transmission assembled in the housing 40 is disassembled to make this deviation small by the combination with other parts, whereafter reassembly must be done. However, this makes the manufacture of the continuously variable transmission cumbersome and cannot achieve a reduction in cost.
Also, in the toroidal type continuously variable transmission provided with the above-described tentative assembling mechanism, the positions of the pin hole, the through-hole and the threaded hole formed in the cam disc, the rolling member and the input disc must be made accurately coincident with one another during the formation of the parts. Therefore, strictness is required of the working of these three parts, and unless this requirement is satisfied, bad working becomes apt to occur. Also, the threaded hole must be formed in the input disc, and this has led to the possibility that damage due to fracture may occur.
Further, in the loading cam device using the knock pin, the magnitude of the frictional force between the knock pin and each pin hole is often not sufficient to compress the pre-load force generating device. Sometimes the integral fixing of the cam disc, the rolling member and the input disc has become unreliable and this has given rise to a hindrance to the incorporating work. Also, in the loading cam device using the threaded hole and the bolt, the deficiency of the compressive force can be prevented, but a force is required of the fastening of a screw and for this reason, the assembling process for the toroidal type continuously variable transmission cannot be simplified.